A fabric obtained by using a composite yarn having a core-sheath cross-sectional shape (hereinafter referred to as a normal core-sheath composite yarn) in which a low-melting polymer is used as a sheath component and an intermingled point of a warp and a weft is fused and fixed through heat treatment has been used for various purposes.
However, in this type of the fabric, a texture is bad (hard), and a low-boiling polymer component appears on the surface of the fabric, decreasing a color fastness or deteriorating a dyeability. Thus, the use of this fabric in clothing is problematic.
On the contrary, as a fabric formed of a core-sheath composite yarn in which a low-melting polymer is used as a core component (hereinafter referred to as an inverted core-sheath composite yarn), only some examples are disclosed. For example, in Japanese Patent Laid-Open No. 220,770/1984, in order to obtain a fabric having a clear wavy uneven pattern and a sharp color difference on the surface, an inverted core-sheath composite yarn is employed in which an ethylene-vinyl acetate copolymer is used as a core component and a polyamide component as a sheath component, respectively. Japanese Patent Laid-Open No. 11,006/1992 discloses the use of a false-twisted yarn formed of an inverted core-sheath composite fiber in which a low-melting polymer is arranged as a core component for developing a sports wear having an improved abrasion-resistant meltability.
The former fabric is obtained by bending and heat-setting. Unless the heat treatment conditions are strictly controlled, the texture of the fabric becomes poor, or the bent portion is weakly fixed. Products except a product having a wavy uneven surface were not applied to any special use. The latter fabric is used to develop clothing which is not broken owing to abrasion by sliding or the like. Although employing the inverted core-sheath composite yarn in which the low-boiling polymer is used as the core component, this composite yarn is not particularly effective at all for moldability and the like of a fabric or clothing.
On the other hand, it has been so far deemed indispensable to coat a melamine resin, an acrylic resin or the like on a surface of a fabric in order to obtain a waterproof fabric which provides a shape stability in pleating, hard finishing or the like and which is suited for an umbrella fabric.
However, the coating with these resins gives a hard texture or some resins cause a trouble such as an offensive odor in heat-molding or the like. In addition to this, in the coating with an acrylic resin or the like, migration of a dye is liable to occur on the coating surface. For example, in an umbrella which is left on a rear window of a vehicle, a dye migrates soon so that the color of the umbrella becomes uneven or a print pattern becomes unclear. Such fatal defects as a product occur.
With respect to a method for obtaining a water-resistant fabric, heat treatment under increased pressure such as calendering or the like is generally known. However, even though a fabric formed of an ordinary polyester yarn is calendered, interstices of intermingled points of a yarn cannot completely be filled, and it is difficult to obtain a great water resistance.
It is an object of the present invention to provide a fabric obtained by using a core-sheath composite yarn and having a shape stability of a good texture and/or a high water resistance, and a novel core-sheath composite yarn which is used in this fabric.
Further, the present inventors have considered that quite a useful final product is obtained by applying the shape stability of the core-sheath composite yarn to a specific use.
For example, a fabric having an excellent surface smoothness can be obtained by heat-treating a woven or knitted fabric obtained by using a covering yarn formed of the core-sheath composite yarn and a urethane elastic yarn under increased pressure. In such a fabric, a fluid resistance to air or water of a wear surface decreases a speed in a swimming race, a skiing race, a snow board race, a bicycle race, a speed skating or the like. Accordingly, a method has been so far known in which a urethane resin is coated on the surface of the fabric or a film is laminated thereon to improve a smoothness.
However, the conventional fabric is poor in moisture permeability and air permeability because of a resin layer or a film layer having few interstices, and involves problems that it has a high density and a great thickness. For this reason, a fabric which has a lighter weight, a better moisture permeability and a better air permeability is deemed preferable as a sports material. Thus, it has been required to obtain a fabric which is excellent in a smoothness and a water resistance without conducting resin coating or film lamination.
Besides, an embossed pattern having a durability can be formed by embossing a fabric made of the core-sheath composite yarn or the like. With respect to the embossing, in general, a hard engraved heat roll and a soft roll combined therewith are rotated under appropriate increased pressure, and a fabric is introduced between these rolls, making it possible to easily apply the uneven pattern to the fabric. However, the form tends to become unclear, and a conventional fabric formed of usual polyester yarns lacks a durability, and the raised and recessed pattern easily decreases or disappears through washing or the like.
In addition, a fiber has been so far known which exhibits a shape stability or the like by fusing a low-melting portion on the surface through heat treatment. However, such a fiber is problematic in that a texture is hardened as mentioned above, and its use has been limited.
Another object of the present invention is to provide quite a useful final product which gives specific function and effect based on a shape stability of a specific core-sheath composite yarn by applying this core-sheath composite yarn to a specific usage and which could not be formed by using the conventional core-sheath composite yarn.